The present application is related to, and claims priority from, Japanese Patent Application No. Hei. 10-200561, the contents of which are incorporated herein by reference.
1. Field of Invention
This invention relates generally to vehicle security systems, and particularly to a vehicle key-verifying apparatus that decreases the chances of vehicle theft.
2. Description of Related Art
Vehicle theft-preventing systems are conventionally known. Such a system typically includes an electronic immobilizing control unit (hereinafter termed an xe2x80x9cimmobilizer ECUxe2x80x9d) that communicates with a transponder incorporated in a vehicle key, and verifies whether data received from the transponder is legitimate. When the data is legitimate, the immobilizer ECU determines that the vehicle key is legitimate and permits starting of the engine. When the data is not legitimate, the immobilizer ECU determines that the vehicle key is not legitimate and prohibits engine starting.
To obtain a high degree of effectiveness in theft prevention, a transponder and an immobilizer ECU of an encrypting type may be utilized. Specifically, as shown in FIG. 12, when the immobilizer ECU provides power to the transponder and transmits query data thereto, the transponder computes response data from function data that is specific authentication data contained in the query data, and sends this response data together with identification data (data for distinguishing the key) to the immobilizer ECU.
Subsequently, the immobilizer ECU relies on the identification data to search its own internal memory for the function data of the transponder, computes auto-response data from this function data and the query data, and collates this auto-response data with the response data from the transponder. When as a result of the collation the two data sets match, the engine is started. However, when the two data sets do not match, the stimulation signal and the query data are sent again, as occasionally a mismatch may occur due to noise or the like despite the key being legitimate. Thereupon, as in the foregoing, the transponder sends the identification data and the response data to the immobilizer ECU, and the immobilizer ECU again collates the auto-response data and the response data.
When an encrypting-type transponder is utilized in this way, even if the response data from the transponder is deciphered by a third party, when the query data from the immobilizer ECU is caused to differ at each iteration, the engine cannot be started even by utilizing the deciphered response data, thereby increasing vehicle security.
However, the sending time from after the immobilizer ECU initiates sending of the stimulation signal and the query data until the reception of the identification data and response data from the transponder corresponding thereto is finished normally requires 100 ms or more. Further, the immobilizer ECU computes the auto-response data before performing collation, but this computing time normally requires 50 ms or more. For this reason, the time required for a single iteration of collation is relatively long, and a considerably long time is required to perform a plurality of collations.
In particular, when the transponder has respective discrete sets of function data, the immobilizer ECU does not know which key has been inserted into the key cylinder until the identification data from the transponder is received, and so the immobilizer ECU cannot search for the function data corresponding to the key within the above-described sending time. Because of this, the need exists to search for the function data in memory on a basis of the identification data sent together with the response data, and thereafter to compute the auto-response data. As a result, subsequent sending performed in a case of a collation mismatch is delayed.
Therefore, it is an object of the present invention to provide a key-verifying apparatus capable of quickly determining that a key is legitimate, even when a key is determined not to be legitimate in at least a first iteration of key-verifying processing due to a communication fault or the like despite a legitimate key having been used.
More particularly, the present invention provides a key-verifying apparatus wherein a query-sending unit sends query data to a transponder attached to a key. A response-receiving unit receives response data from the transponder, and an auto-response generating unit generates auto-response data with respect to the query data. A key-discriminating unit repeats key-verifying processing, wherein collating of two sets of response data up through determination as to whether a key is legitimate is taken to be one iteration, either until the key-discriminating unit determines the key to be legitimate or until a predetermined number of iterations is completed. Further, in an interval after the response-receiving unit has received the response data from the transponder in present key-verifying processing and until the key-discriminating unit finishes discrimination as to whether a key is legitimate, the query-sending unit initiates sending of query data in subsequent key-verifying processing.
With this key-verifying apparatus, sending of subsequent query data is initiated in after receiving the response data in the present key-verifying processing and continues until it is determined whether a key is legitimate. Compared to a system that initiates sending of subsequent query data after it is determined that a key is not legitimate, receipt time for the subsequent response data can be shortened by an amount equal to the time by which the sending-initiation timing of the query data is shortened. Because of this, the entire cycle for performing determination of whether a key is legitimate is shortened.
Consequently, according to the key-verifying apparatus of the present invention, a key can be determined to be legitimate within a short time, even when it is incorrectly determined not to be legitimate in at least a first iteration of key-verifying processing due to a communication fault or the like.